This invention relates to pressure sensitive circuit interrupts in electical capacitors.
Deterioration of a liquid dielectric capacitor generates gases that increase the internal pressure within the sealed capacitor can, causing the walls to bulge and eventually rupture. To prevent rupture and subsequent leakage of the liquid dielectric, pressure sensitive interrupters are used to cause electrical disconnection of the external capacitor terminals from the capacitive element contained within the can.
In previous capacitors employing interrupters (as disclosed, for example, in Rayno, U.s. Pat. No. 3,377,510) the terminals are connected to rivets whose tips extend through holes in an insulating interrupter panel. Foil tabs, connected to the capacitive element, are spot welded to the rivet tips on a side of the interrupter panel opposite the terminals. As the cover of the can bulges, the terminals move outward, drawing the interrupter panel and foil tabs after it. Eventually the motion of the interrupter panel is resisted by downward-facing projections on the cover, causing the welds to break; gases cease to be generated and can rupture is prevented. The cover must often bulge 1/2 inch or more before the welds break.
On occasion, after the welds have broken, the heated gases contract, or dissipate, or are resorbed, permitting the can cover and terminal rivets to settle inward. If the holes in the panel are still aligned with the rivets, there may be physical reconnection between the rivets and the tabs through the holes or, in some cases, electrical arcing between them.